In order to reduce fuel consumption, carbon emissions, and sound nuisance, aircraft manufacturers are attempting to develop electrical systems for driving rotation of aircraft wheels and to incorporate such systems in existing aircraft. The electrical drive systems that have been investigated conventionally comprise an electric motor associated with at least one wheel of an undercarriage and coupler means for selectively coupling and decoupling an outlet shaft of the motor with the rim of the associated wheel. The shaft and the wheel are coupled during stages of taxiing, and they are uncoupled during stages of takeoff, landing, and while the aircraft is in flight.
The design of such a drive system needs to satisfy numerous constraints and to overcome multiple major technical difficulties, some of which are briefly outlined below.
The increase in weight that results from installing the drive system must be as small as possible so that the increase in weight does not outweigh the benefits obtained in terms of reducing the use of fuel.
In order to limit the weight of the drive system, it is desired in particular to simplify the coupler means as much as possible. Drive system architectures in which the coupler means comprise tangential rods actuated by phase shifting two rings via a complex mechanism have been investigated and then discarded.
It is also desired to limit as much as possible the number of drive system parts that are permanently associated with the rim of the wheel, and also to limit their weight, since those parts are subjected to the same mechanical stresses as the wheel (speed, acceleration, shocks, vibration). The use of such parts presents a major impact in evaluating the operating safety of the undercarriage and of the aircraft.
It is naturally also desired to limit as much as possible the mechanical stresses to which the undercarriage is subjected by the parts of the drive system, in order to avoid shortening the lifetime of those parts.
Attempts have also been made to devise a drive system that is compact, since the space available on an undercarriage between the leg of the undercarriage and the wheel is small, in particular because of the presence of the actuator carrier for the wheel brake when the wheel is a braked wheel.
It is also appropriate to develop a drive system suitable for being installed on an already-existing undercarriage without such installation requiring the undercarriage to be modified structurally, and without such installation requiring major modifications to be made to existing wheels and brakes. Such modifications are particularly penalizing for aircraft manufacturers since they involve new development and then performing new certification activities for the undercarriage, the wheels, and the brakes. The costs associated with such new activities can greatly diminish the attractiveness to airlines of such drive systems.